For \(Z^{\prime }\)  mass between \(0.1\,{\rm eV}\)  and the MeV scale, the stellar cooling gives the most important constraints [1]}.
For given stellar object with temperature well above \(M_{Z^{\prime }}\) , the cooling bound on \(g^{\prime }\)  is insensitive to \(M_{Z^{\prime }}\)  because the cooling could occur via off-shell \(Z^{\prime }\)  to neutrinos.
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